Question 1

How does this port scanner work?

Accepted Answer

This tool attempts a TCP connection to each port on your public IP address (detected automatically from your request). If the connection is established, the port is open. If the host sends a TCP RST, the port is closed. If there's no response within 1.5 seconds, the port is filtered. All checks run in parallel, so scanning 12 ports takes about as long as the slowest individual check.

Question 2

What does 'Filtered' mean?

Accepted Answer

Filtered means a firewall or NAT device is silently dropping packets destined for that port — neither accepting nor rejecting the connection. This is the most common state for home networks, where routers block unsolicited inbound traffic by default.

Question 3

Is port scanning my own IP legal?

Accepted Answer

Scanning your own IP address or a server you own is legal and is a standard network administration practice. This tool only scans the IP address of the device making the request — it cannot be used to scan third-party IPs.

Question 4

Why are ports like SSH and RDP marked as 'risky'?

Accepted Answer

Services like SSH (port 22), RDP (port 3389), FTP (port 21), and database ports (3306, 5432, 6379, 27017) are common targets for automated brute-force attacks. If these ports are open on your public IP, they're actively being probed by bots. Consider restricting access via firewall rules, changing to non-standard ports, or disabling these services if not needed.

Question 5

What is port forwarding and how do I test it?

Accepted Answer

Port forwarding is a router configuration that redirects traffic arriving on a public port to a specific device and port on your private network. To test it: configure the forwarding rule on your router, start the service on your local machine, then enter the port number in the checker above. If it shows 'Open', forwarding is working correctly.

Port	Service	Used For
21	FTP	File Transfer Protocol — legacy file sharing
22	SSH	Secure Shell — encrypted remote terminal access
25	SMTP	Simple Mail Transfer Protocol — email sending
53	DNS	Domain Name System — hostname resolution (UDP)
80	HTTP	HyperText Transfer Protocol — unencrypted web
443	HTTPS	HTTP over TLS — encrypted web traffic
3306	MySQL	MySQL database server
3389	RDP	Windows Remote Desktop Protocol
5432	PostgreSQL	PostgreSQL database server
6379	Redis	Redis in-memory cache and message queue
8080	HTTP Alt	Alternative HTTP port, common in development
8443	HTTPS Alt	Alternative HTTPS port
27017	MongoDB	MongoDB document database server

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Common Ports Reference

Frequently Asked Questions